This invention relates to a vertical deflection circuit and, more particularly, to a vertical deflection circuit having a vertical image-position adjustment circuit for vertically adjusting an image position on the screen of a cathode-ray tube (CRT).
An image display device with a CRT, such as a television receiver, is commonly provided with a circuit for vertical adjustment of the position of an image in order to compensate for an image-position deflection originating from deflection of a beam spot of the CRT, or for the purpose of properly correcting the image position as desired.
This image-position adjustment circuit typically has two vertical-output transistors coupled, for example, between both terminals of a DC voltage source in a push-pull manner. These transistors are driven by the output of a vertical drive circuit, and the node of transistors is coupled to a series circuit of a deflection coil, a capacitor and a resistor. A series circuit of a resistor, a variable resistor and another resistor is also coupled between both terminals of the DC voltage source. The node of the deflection coil and the capacitor is coupled to a slidable end of the variable resistor.
With the above arrangement, the output of the vertical-output transistors causes a deflection current to flow across the deflection coil of the image-position adjustment circuit. Further, the direction of the DC deflection current flowing through the deflection coil can be varied by changing the resistance of the variable resistor so that the position of an image on the CRT's screen is vertically adjusted.
In this image-position adjustment circuit, however a parabolic voltage is generated at the node of the deflection coil and the capacitor. This parabolic voltage varies the DC potential at the slidable end of the variable resistor and thus causes a parabolic ripple current to flow through the deflection coil, deforming a displayed image. The circuit disclosed in the Japanese Utility Model Publication No. 56-30043 is designed for a solution to this problem. However, the disclosed circuit cannot completely remove the aforementioned ripple component from the deflection current.